Pressure control system for a grinding machine and actuating unit therefor

ABSTRACT

A mechanically operable control unit for regularly bleeding a fluid line to relieve the pressure of fluid therein. A manipulating handle functions initially to establish an electric circuit through the solenoid winding of a directional valve, the handle functioning thereafter to regulate the flow of fluid through a bleed valve which reduces the pressure by an amount proportional to the forward throw of the handle.

United States Patent Inventor Robert J. Wojcik Melrose Park, Ill.869,071

Oct. 24, 1969 Oct. 19, 1971 Pettibone Corporation Chicago, Ill.

Appl. No. Filed Patented Assignee PRESSURE CONTROL SYSTEM FOR A GRINDINGMACHINE AND ACTUATING UNIT THEREFOR 4 Claims, 7 Drawing Figs.

U.S. Cl

Int. Cl Field of Search 137/560 l-l0lh 9/06 ZOO/61.86; 25 l/DlG. 4;137/560 [56] References Cited UNITED STATES PATENTS 2,675,827 4/1954Craddock 200/61.86 X 3,332,438 8/1967 Abdullaev ZOO/61.86 X

Primary ExaminerRobert K. Schaefer Assistant Examiner-M. Ginsburg VAttorney-Norman H. Gerlach ABSTRACT: A mechanically operable controlunit for regularly bleeding a fluid line to relieve the pressure offluid therein. A manipulating handle functions initially to establish anelectric circuit through the solenoid winding of a directional valve,the handle functioning thereafter to regulate the flow of fluid througha bleed valve which reduces the pressure by an amount proportional tothe forward throw of the handle.

PAIENIEDncI 191ml sum 10F 3 3.514.351

INVENTOR.

ROBERT J. WOJOIK AHorngy Pmm nucr 19 |97l sum 2 or 3 3,614,351

IN V EN TOR. ROBERT J WUJC/K Attorney PAIENTEUncI 1s ism saw 3 or 3INVENTO/P ROBERT J WOJO/K Afforney PRESSURE CONTROL SYSTEM FOR AGRINDING MACHINE AND ACTUATING UNIT THEREFOR The present inventionrelates to a grinding machine of the type wherein the down-pressurewhich is applied to the grinding wheel is in the form of hydraulicpressure which is effective against the grinding wheel boom to force thelatter downwardly and thus cause the grinding wheel to bear against thework with a contact pressure which is proportional to the appliedhydraulic pressure. A grinding machine of this general type is shown anddescribed in and forms the subject matter of 11.8. Pat. No. 3,253,368,granted on May 31, 1966 and entitled Surface Conditioning GrindingMachine." The invention is applicable to a wide variety of grindingmachines which employ hydraulic pressure for pressing the grindingwheels against the work, but in the development thereof, its principleswere specifically adapted to the grinding machine of the aforementionedpatent and, accordingly, for exemplary purposes herein, the invention isdisclosed in the accompanying drawings and described in thisspecification as being operatively associated with such machine forgrinding wheel pres sure control purposes.

In the grinding machine of aforementioned US. Pat. No. 3,253,368, aswell as in various other grinding machines wherein the down-pressure ofthe grinding wheel on the work is effected by fluid pressure, suchpressure is substantially constant, at least during any given grindingoperation, as, for example, during the surfacing of a particular steelbillet or the like. The actual contact pressure which is maintained onthe billet by the grinding wheel is a combination of two factors,namely, a gravitational force which is incident to the combined weightof the boom and the grinding wheel on the boom, and the hydraulic forcewhich is applied to the boom in a downward direction. Except for theprovision of an adjustable pressure regulating valve which determinesthe fluid pressure in the hydraulic system and against the boom andordinarily is regulated prior to any given grinding operation, no meansis provided for readily altering the down-pressure on the grinding wheelduring actual grinding of a billet or other work. Although it ispossible for a second operator to effect a change in the setting of thepressure regulating valve under the direction of the operator of thegrinding wheel, such a procedure is not altogether satisfactory sincethere frequently is a need for an instantaneous pressure change whengrinding the surface of a given billet. Even if the pressure regulatingvalve were to be positioned within reach of the grinding machineoperator, the effect of a conventional pressure regulating valve is notrapid enough to produce the desired change in pressure of the grindingwheel in time to take effect on the particular location on the surfaceof the billet being ground where the greater or lesser pressure is to beapplied, especially during a rapid traverse of the billet by thegrinding wheel. Furthermore, the manual control knob, dial or otherpressure regulating element which is ordinarily associated with aconventional pressure regulator is not sensitive enough that theoperator may ascertain the necessary degree of manipulation which isrequired to produce the desired pressure change.

The pressure control system of the present invention embodies aregulable pressure bleeder valve which is capable of adjustment on thepart of the operator of the grinding machine and by means of which alimited portion of the hydraulic pressure which is applied to thegrinding wheel by way of the usual directional valve and boom cylindermay instantaneously be bled t the atmosphere or sump and at a ratecommensurate with the desired down-pressure which is to be maintained bythe grinding wheel on the billet or other work being conditioned orground. The effect of thus bleeding the applied pressure issubstantially instantaneous throughout the hydraulic system so that anyadjustment of the pressure bleeding valve is effective immediately toreduce the down-pressure of the grinding wheel. Conversely, a reductionin the bleeding effect of the pressure regulating valve is substantiallyinstantaneously translated into an increase in the down-pressure on thegrinding wheel.

The present invention further embodies a novel control unit the functionof which is initially to actuate both the usual directional valve bymeans of which fluid is supplied to the boom cylinder and the pressurebleeder valve. Such unit is electrically connected to thesolenoid-actuated directional valve and is hydraulically connected tothe pressure bleeder valve. The unit is provided with a relatively longcontrol lever having a control knob at its distal end so that the throwof the lever may be regulated within very fine limits. The lever isspring-biased to a retracted position and the unit is positioned infront of the operator of the grinding machine and on the control panelthereof so that operation of the lever is effected by the simpleexpedient of pulling or swinging the lever rearwardly. After the leverhas been thus advanced through a small angle, an internal cam serves toclose the contacts which are associated with a control switch, suchclosure of the contacts serving to establish an electric circuit throughthe solenoid winding of the directional valve which supplies fluid underpressure to the boom cylinder for forcing the boom downwardly to applypressure to the billet by the grinding wheel. Thereafter, furtherrearward movement of the control lever maintains the contacts of thelimit switch in their closed condition and, as a consequence, maintainsthe directional valve energized. The same cam which actuates the limitswitch also progressively actuates the pressure bleeder valve, theadvancing forward movements of the lever serving progressively toincrease the size of the bleeder valve orifice, thus increasing thebleeding efi'ect and progressively reducing the down-pressure of thegrinding wheel. The maximum throw of the control lever is on the orderof and, because the lever has a relatively long effective extent, theoperatoris afforded relatively wide increments of adjustment to effectsmall increments of pressure bleeding. After a small amount ofexperience, a competent operator is able to manipulate the lever by hissense of feeling and without visualization thereof so as to attain adesired grinding wheel pressure against the billet within very finelimits.

The provision of a pressure control system and actuating I unit thereforsuch as has briefly been outlined above constitutes the principle objectof the present invention.

The provision for a pressure bleeder valve of an actuating unit which isextremely simple in its construction and may, therefore, be manufacturedat a relatively low cost; one which is rugged and durable and,therefore, will withstand rough usage; one which is comprised of aminimum number of parts, especially moving parts and, therefore, isunlikely to get out of order; one which is capable of ease of assemblyand dismantlement for purposes of inspection of parts, replacement orrepair thereof; one which is smooth and silent in its operation; onewhich when unattended either by accident or purposely will result in araising of the grinding wheel from the billet or other work undergoinggrinding; and one which, otherwise, is well adapted to perform theservices required of it, are further desirable features which have beenborne in mind in the production and development of the presentinvention.

Other objects of the invention and the various advantages andcharacteristics of the present control system and actuating unittherefor will be apparent from a consideration of the following detaileddescription.

The invention consists in the several novel features which arehereinafter setforth and are more particularly defined by claims at theconclusion hereof.

in the accompanying three sheets of drawings forming a part of thisspecification, one illustrative embodiment of the invention is shown.

In these drawings:

FIG. 1 is a front perspective view of a grinding machine having appliedthereto a pressure control system and actuating unit embodying themachine being shown in operation upon a steel billet;

FIG. 2 is an enlarged top plan view of a pressure bleeding valveactuating unit which is employed in connection with the presentinvention, a portion of the unit casing being broken away in order moreclearly to reveal the nature of the associated valve control mechanism;

FIG. 3 is a side elevational view of the unit with a portion of the unitcasing removed in the interest of clarity;

FIG. 4 is a front elevational view of the unit with a portion of theunit casing removed;

FIG. 5 is an enlarged sectional view taken on the line 5-5 of FIG. 3;

FIG. 6 is an enlarged rear perspective view of the actuating unit with aportion of the unit casing broken away; and

FIG. 7 is a combined electric and hydraulic circuit diagram of theimproved pressure control system.

Referring now to the drawings in detail and in particular to FIG. 1wherein an exemplary form of grinding machine which is capable ofaccommodating the pressure control system of the present invention isshown, this machine is designated in its entirety by the referencenumeral 10 and is of the type which is shown and described inaforementioned U.S. Pat. No. 3,253,368. The disclosure of the grindingmachine 10 is somewhat schematic in its representation, the illustrationof FIG. 1 being made with a view toward establishing an exemplaryenvironment for the presentcontrol system and, therefore, many of thedetails of the grinding machine which bear no relation to the inventionhave purposely been omitted. For a full understanding of the operationof the machine 10, reference may be had to said US. PatrNo. 3,253,268.

The grinding machine 10 is shown in FIG. 1 as being in operation uponthe upper surface of a steel billet B which is operatively supportedupon a suitable pallet structure 12. Said grinding machine employs asingle grinding wheel 14 which preferably but not necessarily rotatesabout a horizontal axis extending parallel to the longitudinal axis ofthe billet B and is carried at the forward or outer end of a boom 16.The latter is mounted on a boom housing 18 to which there is secured amotor carriage 20 which supports an electric motor M. Said motoroperates through a speed reducing transmission 22 to drive the grindingwheel 14 by means of a belt and pulley connection 24. The boom housing18 is pivoted at its medial regions for rocking movement in afore-and-aft direction on a shaft 26 which is carried by a boom carriage30. The latter is in the form of an II-shaped casting which is slidablein a foreand-aft direction on two spaced apart horizontally extendingguide rails 32 certain portions of which overlie and are spaced abovethe billet supporting pallet structure 12. The guide rails 32 have theirfront ends supported on a tail stock carriage 34 which travels on afixedly mounted, horizontally extending, elevated rail 36. The rear endsof the guide rails 32 are supported on the upper region of a machinebase assembly 40 which travels on a pair of spaced apart, horizontalrails 42 and is driven by a reversible combined hydraulic motor and gearreduction device 44, the latter being supplied with fluid from a pump46. The machine base assembly 40 embodies an operator's control cab 48within which there is disposed a control panel 50 having manuallyoperated control instrumentalities by means of which the above-mentionedtraction drive instrumentalities for the machine base assembly 40 may beactuated in order selectively to move the same in either direction alongthe rails 42, and also by means of which various other grinding machinefunctions may be controlled.

In order to impart tilting movements to the boom housing 18 for thepurpose of raising and lowering the grinding wheel 14 from the billet Bundergoing grinding or conditioning, an hydraulic boom cylinder 52 ispivotally connected to the forward end of the boom 16. An upstandingplunger 54 carrying a piston 56 (see FIG. 7) at its lower end projectsupwardly 7 boom housing 18 will be swung bodily as a unit in onedirection to lower the grinding wheel 14. Conversely, when pressurefluid is supplied to the upper end of the cylinder 52 so as to retractthe cylinder upwardly, the boom housing 18 will be swung in the oppositedirection to raise the grinding wheel. The means for selectivelysupplying fluid to the boom cylinder 52 to effect such swingingmovements of the boom housing and for bleeding the pressure of fluidsupplied to the cylinder during down-pressure of the grinding wheel onthe billet B constitutes the subject matter of the present invention andwill be described in detail presently.

The fore-and-aft movements of the boom carriage 30 are effected underthe control of two hydraulic cylinders 62 which are secured to and movewith said boom carriage. Fluid under pressure for operating thecylinders 62 is supplied by the previously mentioned pump 60 which alsosupplies pressure fluid for actuating the boom cylinder 52 as previouslydescribed. Hydraulic mechanism is provided for the selective admissionof fluid under pressure to the opposite ends of the cylinders 62 foractuating the same, such mechanism bearing no relation to the presentinvention and consequently being not illustrated herein, it beingsufficient to state that such mechanism is operated under the control ofcertain of the previously mentioned manually operated controlinstrumentalities on the control panel 50. Various other operatingmechanisms and control devices for effecting certain grinding machinefunctions appear in FIG. 1 but have not been described herein since theylikewise bear no relation to the present invention.

It will be understood that during the grinding operation on a givenbillet B, the operator in the cab 48 is able to traverse the billet withthe grinding wheel 14 in a longitudinal direction by causing the machinebase assembly 40 to travelon the rails 42, the grinding wheel to moveover the upper surface of the billet in a longitudinal direction. Byselectively supplying pressure fluid to the cylinders 62, the grindingwheel 14 may be brought into register with any selected transverseregion of the billet. The attainment of a desired grinding pressure ofthe grinding wheel 14 upon the upper surface of a billet B is effectedby causing energization of the motor M2 so as to actuate the pump 60 andthereafter causing the fluid under pressure which is generated by thepump to be conducted to the cylinder 52 while simultaneously bleedingsuch fluid to the atmosphere or a sump at a selected rate of bleeding,all in a manner that will now be set forth in detail.

In FIG. 7, the electric and hydraulic circuitry by means of which thegrinding pressure of the grinding wheel on the billet B is attained isdisclosed and the functioning of the electric and hydraulicinstrumentalities is effected under the control of a single actuatingunit 70, the details of which are illustrated in FIGS. 2 to 6,inclusive. The actuating unit 70 will be described in detailsubsequently but for purposes of discussion of the circuit diagram ofFIG. 7, it is deemed sufiicient to state that this actuating unitembodies a manually operable cam 72 which is yieldingly biased by meansof a helical tension spring 74 to the retracted position in which it isshown in full lines in FIGS. 3 and 7. Said cam is capable of beingshifted in a clockwise direction as viewed in FIGS. 3 and 7 from suchretracted posi-- tion to a fully advanced position. A manually operablecontrol lever 76 is provided for manually actuating the cam 72. After ashort initial idle movement of the cam 72, a control switch CS isactuated to cause energization of a solenoid-actuated directional valve.DV which then directs pressure fluid to the boom cylinder 52 from thepump 60 thus causing lowering of the boom 16 and its associated grindingwheel 14 to the end that sand grinding wheel contacts the billet B.- Atthe time of initial actuation of the switch CS and consequentenergization of the solenoid-actuated directional valve DV, a bleedervalve I BV in associated relation with the actuating unit 70 has itsorifice opening 78 (see FIG. 5) fully opened and serves to bleed theapplied pressure fluid in the boom cylinder to such an extent that apredetermined minimum pressure on the billet B is maintained by thegrinding wheel 14. Further movement of the cam 72 serves to maintain thedirectional valve DV energized, while at the same time the bleeder valveBV progressively decreases the size of its orifice opening so that thepressure of fluid under pressure acting on the grinding wheel isprogressively increased from the minimum pressure to a maximum pressurefor which the bleeder valve BV is predeterminedly set.

Specifically, and with reference to FIG. 7, upon closure of a masterswitch MS, an electric circuit is established for the motor M2, thiscircuit extending from a suitable electrical source C which may be acommercial power line, through the master switch MS, leads 1], 13, themotor M2, leads and 17, and the master switch MS, back to theaforementioned electrical source C. Energization of the motor M2 servescontinuously to drive the pump 60.

Upon actuation of the control switch CS by the cam 72, an electriccircuit is established so as to actuate the directional valve DV, thiscircuit extending from the current source C, through the master switchMS, the lead 11, a lead 19, the switch CS, a lead 21, the solenoidwinding w of the directional valve DV, a lead 23, the lead 17 and themaster switch MS, back to the electrical source C. Energization of thewinding w actuates the directional valve DV so that hydraulic fluidflows from the sump S, through the pump 60, the bleeder valve BV, acheck valve CV, a pressure grading valve PGV into the lower end of thecylinder 52, thus forcible moving the latter downwardly and applyingpressure to the boom 16 so as to cause the grinding wheel 14 to beforced against the billet B. At this time, the orifice 78 of the bleedervalve BV is at its maximum opening as previously set forth so that thepressure maintained by the grinding wheel 14 on the billet B is at itsminimum.

As the cam 72 is turned in a clockwise direction as viewed in FIGS. 3and 7 by pulling the control lever 76 toward the operator of thegrinding machine, the orifice opening 78 is proportionately decreased,thus resulting in a gradual decrease of the bleeding action and aconsequent gradual increase in the pressure of fluid in the lower regionof the cylinder 52. By the time that the cam 72 has attained its fullyadvanced position, the orifice opening 78 of the bleeder valve BV is atits minimum and the bleeding action is such that maximum fluid pressureis maintained in the lower region of the cylinder 52 while the grindingwheel 14 is caused to bear against the billet with maximum grindingpressure.

By means of the electric and hydraulic circuitry which is shown in FIG.7 and described above, the operator of the grinding machine may, byproper manipulation of the control lever 76, cause the grinding wheel 14to exert varying grinding pressure upon the billet B during any giventraverse of the wheel longitudinally over the billet. During spotgrinding operations as explained in aforementioned US. Pat. No.

3,253,368, the necessary initial heavy pressure, followed byincreasingly lighter pressures, may be applied to any given area of thebillet undergoing treatment, lighter pressures being attained by movingthe control lever 76 away from the operator (counterclockwise as viewedin FIGS. 3 and 7) and heavier pressures being attained by moving thelever in the reverse direction (clockwise as viewed in FIGS. 3 and 7).If at any time the operator releases the control lever 76, The tensionspring 74 will restore the cam 72 to its retracted position wherein thecontrol switch CS is disengaged from the cam 72 and the circuit for thesolenoid winding of the solenoid-actuated directional valve DV isdeenergized, so that the directional valve DV is shifted to its normalposition wherein the upper end of the cylinder 52 is bled to the sump Sand substantially full pump pressure is applied to the upper end of thecylinder. Under such a condition, consequent upward movement of thecylinder 52 will restore the boom 16 and the grinding wheel 14 to theirraised positions.

The pressure grading valve PGV is provided for the purpose of allowingthe grinding wheel 14 to follow the contour of the upper surface of abillet B undergoing grinding in the event that such surface is not trulyplanar, as, for example, when the surface is of an undulatory nature orcharacter. The valve PGV is provided with a piston slide which is biasedby way of a helical spring 82, the valve being so disposed that in itsnormal position it conducts fluid under pressure from the check valve CVinto the lower end of the cylinder 52. At such time as a marked increasein the pressure occurs in the lower end of the cylinder due to upwardmovement of the grinding wheel 14 and the boom 16 when the former ridesupwardly on a given undulation in the upper surface of the billet B, theposition of the piston slide 80 is changed so that a portion of thepressure is discharged to the sump S through a regulating valve RVhaving a manually controlled valve orifice 84. The function of thepressure grading valve PGV and the regulating valve RV, therefore, is,broadly speaking, to maintain a substantially constant down-pressure onthe grinding wheel 14 commensurate with the position of the controllever 76 of the actuating unit 70 despite the presence of undulations inthe upper surface of the billet being ground or conditioned. In theoperation of the pressure grading valve PGV, as soon as a givenundulation has been traversed by the grinding wheel l4 and the latter isrestored to its normal level, the piston slide 80 of the valve PGV isreturned to its normal position by means of the spring 82.

Considering now the mechanical organization of the actuating unit 70,and referring to FIGS. 2 to 6, inclusive, this unit embodies a flatrectangular baseplate having comer bolt holes 102 by means of which itmay be fixedly secured by bolts such as are indicated at 104 in FIGS. 2,3 and 4 to the control panel 50 (see FIG. 1) in such a manner that theaforementioned control lever 76 assumes a position remote from theoperator of the grinding machine and is capable of being pulled towardthe operator to effect progressive narrowing of the valve orifice 78(see FIGS. 5 and 7). To facilitate manipulation of the control lever 76,a knob 106 is disposed on the outer or distal end of said lever.

A reinforcing plate 108 overlies the base plate 100 and is secured inposition thereon by screws 110. An inverted cupshaped housing 112 havingfront and rear walls 114 and 116 and an arched top wall 118 which may beintegrally formed with the walls 114 and 116, is further provided withside walls 120 and 122. The lower edge regions of the various walls 114,

116, 120 and 122 4The secured by screws 124 to the sides of the plate108, the latter plate constituting a bottom wall for the housing 112.The aforementioned control switch CS is secured in an opening 126 in theplate 108 and the lower region thereof projects through aligned openings128 and 130 (see FIG. 3) in the plate 108 and the panel 50,respectively. The control switch CS is provided with a verticallyslidable, depressible, contact-actuating plunger 132 which carries atits upper end a roller 134. The latter is normally disposed in the pathof movement in the aforementioned cam 72 for actuation thereby as willbe described in detail presently. A medially disposed, verticallyextending, partition wall extends transversely between the front andrear walls 114, 116 of the housing as best seen in FIG. 2 and serves tosupport one end of a hollow, horizontally extending rock shaft 142, theshaft being provided at its inner end with a thickened hub portion 144(see FIG. 5) which is rotatably mounted in a bearing opening 146 in thepartition wall 140. The outer end of the rock shaft is rotatablydisposed in a bearing opening 148 in the side wall 120 of the housing112. The rim of the outer end of the hollow rock shaft 142 hasformedtherein an annular series of adjusting slots 150 the function of whichwill be set forth presently.

The cam 72 is operatively mounted on the rock shaft 142 and is fixedlysecured thereto for movement bodily therewith by means of a set screw152 which is disposed in a threaded radial bore 154 in said cam. Thelatter is in the form of a relatively thick flat platelike member havingan arcuate cam surface 156 of uniform curvature, and a flat surface 158.The control lever 76 has its proximate end threadedly received in asocket 160 in the cam 72, and this lever projects outwardly of thehousing 112 through an arcuate clearance slot 162 in the arched top wall118, as well as in a portion of the front wall 114 of the housing 112.The cam 72 is further provided with a contact edge 166 which is designedfor contact with a limit stop in the form of a bolt 168. The latter iscarried by the partition wall 140 of the housing 1 12. The helicaltension spring 74 which normally maintains the cam 72 in its retractedposition has one end thereof anchored on a cross rod 169 and has itsother end secured to a transverse pin 171 on the cam 72. The cross rod169 extends horizontally and has its ends disposed in holes in thehousing walls 120 and 140 and also provided with nuts in order to holdit in place and against lateral displacement.

The thickened hub portion 144 of the rock shaft 142 is provided with anaxially disposed, noncircular opening 170 and thus receives thecorrespondingly shaped or flattened end por- I tion 172 of a rotatablevalve stem 174 which is associated with and forms a part of theaforementioned bleeder valve BV. This bleeder valve is shown in detailin FIG. and it involves in its general organization a valve body 175which is of generally T- shaped design and has a fluid inlet leg 178 anda fluid outlet leg 180 in alignment therewith. The two legs communicatewith each other internally of the valve body 176 through a valve seat182 which, in combination with a valve needle 184 on the adjacent end ofthe valve stem 174, defines the aforementioned adjustable orifice 78(see FIG. 7). The medial region of the valve stem 174 is threadedlyreceived as at 179 in a third leg 185 of the valve body 176 of thebleeder valve BV. The rotatable valve stem 174 projects through aconventional packing gland 186 in the leg 185 of the valve body 176, andthe bleeder valve BV as a unit is fixedly mounted on the sidewall 122 ofthe housing 112 by an assembly 188 which comprises a nut and also a pairof washers on opposite sides of a mounting plate 190, the latter beingsecured by screws 192 to the sidewall 122. The packing gland 186 is heldin place by way of a nut 189 on the third housing leg 185. Aconventional nipple fitting 194 connects the housing leg 178 to a fluidline leading to the pressure side of the pump 60 and aconventionalnipple fitting 196 connects the outlet leg 180 to the pressure gradingvalve PGV, in the manner and for the purpose heretofore set forth inconnection with the circuit diagram of FIG. 7.

In the operation of the grinding machine and with the bleeder valve BVoperatively connected to the pump 60 and the pressure grading valve PGVas previously described, the flat clearance surface 158 of the cam 72(see FIG. 3) normally opposes but does not engage the roller 134 of thecontrol switch CS inasmuch as the helical tension spring 174 serves tomaintain the cam in its retracted position. At such time the grindingwheel 14 remains elevated above the level of the billet B. After theoperator has brought the machine base as sembly 40 and the tail stockcarriage 34 to a position wherein the grinding wheel is in properregister with the billet, and at the desired location for commencementof grinding operations, the control lever 76 of the actuating unit 70 ispulled rearwardly towards the operator and positioned at an angle which,from previous experience, the operator has found will yield a desirableand normal grinding pressure for the grinding wheel on the upper surfaceof the billet B. Assuming for purposes of description that such aposition of the control lever 76 is one wherein the lever projectsradially outwardly through the slot 162 (see FIG. 3) at the midpoint ofthe latter, the consequent rotational movement of the cam 72 and thevalve stem 174 will have positioned the valve needle 184 (see FIG. 5) sothat the valve orifice 78 will yield a bleeding action through thebleeder valve BV which is adequate to reduce the otherwise excessivegrinding pressure in the lower'end of the cylinder 52 and also to attainthe desired normal grinding pressure. it will be understood that duringthis pulling of the control lever 76 to its midposition in the slot 162,the clearance between the roller 134 of the control switch CS and theflat surface 158 on the cam 72 willhave initially been taken up and theroller will have moved onto the arcuate cam surface 156 of the cam, thuscausing the contacts of the limit switch to become closed so as toenergize the electric circuit for the winding w of the directional valveDV which is disposed in the circuit in series with the control switch CSas previously described. Energization of the directional valve DVdirects fluid under pressure to the lower end of the cylinder aslikewise described. The extent of the bleeding action of the bleedervalve BV is, of course, a function of the size of the orifice 78 which,in turn, is a function of the position of the control lever 76. Aspreviously stated, with the lever in its midposition, the size of theorifice 78 is such that precisely the correct rate of cylinder bleedingwill take place to maintain the pressure of fluid in the lower end ofthe cylinder 52 constant and at the optimum pressure for normal billetgrinding. While maintaining the control lever 76 thus positioned, theoperator may effect the necessary traverse operations to effectprogressive grinding of the entire upper surface of the billet. If thegrinding machine is equipped with automatic traverse facilities, it ismerely necessary for the operator to maintain the control lever 76 inits midposition and the carriage movements will be such as eventually tocomplete the grinding of the entire upper surface of the billet Bwithout further attention on his part.

The fact that the upper surface of the billet B may be of an undulatorynature requires no change in the setting of the control lever 76inasmuch as the previously described pressure grading valve PGV willfunction as previously set forth to shift the piston slide 80 to theleft as viewed in FIG. 7 each time an automatic pressure increase isencountered in the lower end of the cylinder 52 due to-the upwardmovement of the grinding wheel 14 as the wheel enters a region of raisedbillet surface elevation. Under such circumstances, a constant grindingwheel pressure will be maintained against the billet. However, if aparticular billet has been marked at the spotting station prior topresentation to the grinding machine, the operator, upon encounteringthe crest region of a given undulation, may shift the control lever 76in a rearward direction, thereby decreasing the size of the orificeopening 78 and thereby decrease the bleeding action of the bleeder valveBV and increase the pressure in the lower end of the boom cylinder 52 tothe end that a more efficient grinding pressure on the raised surface ofthe billet will be attained. Conversely, if during a given traverse ofthe billet by the grinding wheel 14, a soft spot or region isencountered, the operator may shift the position of the control lever 76forwardly to decrease the size of the orifice 78 and thereby increasethe bleeding action of the bleeder valve BV, thus attaining a lightergrinding pressure of the grinding wheel on the surface of the billet B.Manipulation of the control handle 76 of the actuating unit will befound particularly useful in connection with spot grinding operationsinasmuch as during the oscillatory movement of the grinding wheel in thevicinity of a given area of the upper surface of the billet as describedin previously mentioned US. Pat. No. 3,253,368, an optimum grindingpressure of the grinding wheel on the billet during grinding wheeloscillation'may be maintained at the discretion of the operator byshifting the control lever 76 in one direction or the other.

The biasing spring 74 not only maintains the control lever 76 in itsretracted position with the cam 72 out of contact with the roller 134 ofthe control switch CS so that the grinding machine cannot be left inoperation if the operator leaves the cab 48, but it also functions inthe manner of a dead man's stick to terminate operation of the grindingmachine in the event that the operator becomes incapacitated due to anaccident or for any other reason.

The invention is not to be limited to the exact arrangement of partsshown in the accompanying drawings or described in 1. ln an actuatingunit of the character described, in combination, a housing having abottomwall, a rear wall, a front wall, upstanding sidewalls, a top wall,and a partition wall extending between said front and rear walls, ahorizontally disposed rock shaft projecting between said partition walland one of the side walls and rotatably joumaled therein, a cam securedto said rock shaft and confined between said partition wall and said onesidewall, said top wall being formed with a slot therein, a controllever projecting radially outwardly from said cam and extending throughsaid slot for manipulation exteriorly of the housing, a fluid valvemounted on the other sidewall and having a valve body establishing apair of communicating legs which are disposed exteriorly of the housingand a third leg which projects through the other sidewall, a valve seatdefining a valve orifice through which the legs of said pair of legscommunicate, a valve stem threadedly disposed within said third leg formovement toward and away from said seat upon rotation of the stem inopposite directions to vary the effective size of said orifice, saidstem projecting inwardly of the housing and being coaxial with said rockshaft, means establishing a driving connection between the rock shaftand the valve stem whereby rotational movement of the rock shaft ineither direction will effect corresponding turning movements of saidstem, said cam being provided with an arcuate cam surface thereon, and acontrol switch having a depressible actuating plunger positioned in thepath of movement of said arcuate cam surface, said cam and rock shaftbeing movable between a fully retracted position wherein said valveorifice is of maximum size and said cam surface is out of engagementwith said plunger, and a fully advanced position wherein the valveorifice is of minimum size and the actuating plunger is engaged anddepressed by said cam surface.

2. In an actuating unit of the character described, the combination setforth in claim 1 and wherein said cam is formed with a clearance surfacethereon which is effective to maintain the cam surface out of engagementwith said plunger until the cam has been moved from its fully retractedposition toward its advanced position throughout a small angular extentof turning movement.

3. In an actuating unit of the character described, the combination setforth in claim 2 and including, additionally, spring means yieldinglybiasing said cam and rock shaft toward their fully retracted positions.

4. In an actuating unit of the character described, the combination setforth in claim 3 and wherein said cam is capable of rotationaladjustment with respect to the rock shaft and is secured thereto inadjusted relationship by a set screw which projects radially through thecam.

1. In an actuating unit of the character described, in combination, ahousing having a bottom wall, a rear wall, a front wall, upstandingsidewalls, a top wall, and a partition wall extending between said frontand rear walls, a horizontally disposed rock shaft projecting betweensaid partition wall and one of the side walls and rotatably journaledtherein, a cam secured to said rock shaft and confined between saidpartition wall and said one sidewall, said top wall being formed with aslot therein, a control lever projecting radially outwardly from saidcam and extending through said slot for manipulation exteriorly of thehousing, a fluid valve mounted on the other sidewall and having a valvebody establishing a pair of communicating legs which are disposedexteriorly of the housing and a third leg which projects through theother sidewall, a valve seat defining a valve orifice through which thelegs of said pair of legs communicate, a valve stem threadedly disposedwithin said third leg for movement toward and away from said seat uponrotation of the stem in opposite directions to vary the effective sizeof said orifice, said stem projecting inwardly of the housing and beingcoaxial with said rock shaft, means establishing a driving connectionbetween the rock shaft and the valve stem whereby rotational movement ofthe rock shaft in either direction will effect corresponding turningmovements of said stem, said cam being provided with an arcuate camsurface thereon, and a control switch having a depressible actuatingplunger positioned in the path of movement of said arcuate cam surface,said cam and rock shaft being movable between a fully retracted positionwherein said valve orifice is of maximum size and said cam surface isout of engagement with said plunger, and a fully advanced positionwherein the valve orifice is of minimum size and the actuating plungeris engaged and depressed by said cam surface.
 2. In an actuating unit ofthe character described, the combination set forth in claim 1 andwherein said cam is formed with a clearance surface thereon which iseffective to maintain the cam surface out of engagement with saidplunger until the cam has been moved from its fully retracted positiontoward its advanced position throughout a small angular extent ofturning movement.
 3. In an actuating unit of the character described,the combination set forth in claim 2 and including, additionally, springmeans yieldingly biasing said cam and rock shaft toward their fullyretracted positions.
 4. In an actuating unit of the character described,the combination set forth in claim 3 and wherein said cam is capable ofrotational adjustment with respect to the rock shaft and is securedthereto in adjusted relationship by a set screw which projects radiallythrough the cam.